1. The Field of the Invention
This invention relates to facsimile transmission over a network structure. More, particularly, this invention relates to facsimile transmission over a wireless communication channel wherein the wireless communication channel may exhibit fading and channel interference.
2. Description of Related Art
Thomas et al., U.S. Pat. No. 5,649,001, which is hereby incorporated by reference in its entirety for the material disclosed therein, discloses a reconfigurable communication interface device to identify a valid communication adaptor cable.
3. Present State of the Art
Traditional facsimile transmissions have occurred over wired communication channels such as those characteristic of the public switch telephone network (PSTN). While such wired communication channels may be susceptible to interfering signals, interference on such hard wired communication channels is generally minimal. As such, facsimile transmission rates generally keep pace with technological advancements in modulation theory. For example, traditional facsimiles were transmitted at baud rates consistent with those of data modem transmissions. As modulation techniques for data modems advanced, so also did facsimile transmission techniques. Modernly, data transmission techniques may employ modulation rates in excess of 56.6 kilobits per second. Such high modulation rates require minimal noise injection onto the communication channel. As modulation data rates increase, the coding or frequency spacing between information bits becomes more narrow and therefore more congested. Therefore, high modulation data rate techniques require robust communication channels for reliable transmission of high data rate data.
Technological advancements, in parallel with those of modulation advancements such as facsimile and data transmissions, have also occurred in the area of wireless communication. One such example were wireless technologies have become ubiquitous relates to cellular telephony. Cellular telephony, or more broadly wireless communication, enables a user to roam freely within a designated zone and establish a wireless communication channel with a remote party. Because of the roaming freedom available to a cellular telephone user, wireless communication channels exhibit varying levels of interfering noise, and hence reliability, during a particular communication session. In fact, during a particular transmission session a cellular user may widely roam, thereby subjecting the wireless communication channel to varying and ofttimes unpredictable levels of noise or interference.
In a communication session between a cellular telephone user and a remote party wherein the session parties are exchanging analog voice information, variations and interference are often tolerable due to the context nature of voice communication. Additionally, cellular users may also recognize the presence of interference due to their present location or orientation and institute corrective measures, such as repositioning the cellular transceiver to a more favorable location. When interference adversely affects a wireless voice communication session, a user may simply request that the other party repeat the previous statement.
As cellular technology advanced, cellular transceivers incorporated capability for facilitating transmission of data information across the established wireless communication channel. As a data transmitter and receiver, a facsimile machine became a candidate for interfacing with a cellular transceiver for sending and receiving facsimiles. Cellular transceiver users transceiving facsimiles over cellular networks have become frustrated with the unreliability of transmissions primarily due to the interference impairments of wireless communication channels. Modern facsimile protocols recognize that impairments to communication channels result in injected errors within the facsimile transmission. At least one such facsimile protocol incorporates an error correction mode (ECM) wherein a block of facsimile data is partitioned and appended with a cyclically redundant code (CRC). A facsimile receiver, upon receipt of the partitioned block and appended CRC, evaluates the sequencing of data within the partitioned block and compares that sequencing against the corresponding appended CRC. When the CRC does not match the pattern as generated from the received data, an error in the transmitted data is detected. Techniques exist for accepting a predetermined number of errors in facsimile data without requesting the transmitting entity to retransmit the previous portion of facsimile data.
In wireless communication channels, however, typical interference frequently injects a substantial number of errors into the transmitted facsimile data portion, thus prohibiting a facsimile receiver from accepting that portion of the facsimile data. Such rejection causes the transmitter to retransmit the previous block of facsimile data. Frequently, a subsequent retransmission fares only as well as the previous transmission due to the characteristics of a wireless communication channel. Typically the result of such a scenario is that a transmitter and receiver continuously retransmit the same block of facsimile data until one party recognizes the futility of the present situation. As illustrated in FIG. 1, a facsimile machine may take the form of an integrated device such as facsimile machine 110 or alternatively, may take the form of a host 100 such as a personal computer coupled to a fax modem 102 for performing the integrated facsimile function. As illustrated by FIG. 1, a facsimile machine 110 and a facsimile machine 112 comprised of a host and a fax modem, interoperate and communicate via wired communication channels 104 and 108 interconnected via a communication network 106 such as a public switched telephone network. Because of the wired connection between facsimile machines, minimal noise is injected into the communication channels thereby facilitating modulation techniques employing higher data rate techniques. While such high data rate modulation techniques may be adequate for wired communication channels, wireless communication channels, however, are far more susceptible to interference.
Thus, it appears that there exists no present technique for a facsimile machine to detect transmission of facsimile data over a wireless communication channel and modify the characteristics of the transmission of such facsimile data in such a manner to more reliably deliver facsimile data to a recipient facsimile machine. Furthermore, there does not currently exist techniques for determining the characteristic of the communication channel through which facsimile data will be transmitted and therefrom modify a retransmission criterion, recognizing that wireless communication channels may sustain an enhanced interference level for a subtained period of time. Therefore, a need exists for providing a method and system for recognizing a wireless communication channel as the channel through which facsimile data will be transmitted and accordingly modify accordingly the transmission characteristics of such a transmission of facsimile data.